Hello, I want to share some of my ideas about game after playing it. I am software developer and gamer so it’s not newbie ideas 
and sorry about my poor english.
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Monolith/Echoes locations need vertical layout sometimes, now they are literally flat. Well sometimes few very low cliffs, but thats all. You can do more interesting things, I mean for example in ‘the end of time’ location we have stairs up to the second floor (near Arlos aka Nana your business). So plain end game locations can be more interesting with that.
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Similiar to p1.: we can emulate vertical progression with entrances to diff location zones like in campaign, when after some light we enter kind of room. With same appearens or another we can go undeground or higher.
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Dungeons.: dungeons is fun, few more interesting dungeons would be great.
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Arena keys: to much of them in echoes reward. Reduce drop and appearence at least ten times lower and arena dungeon not very fun, sorry. I didn’t complete all 10 timelines and have 10+ arena keys just from drop.
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Quests/Events in monolith: add some activity into echoes, may be some unpredictable changes like ‘we have unique mob dropper here, find it if u can’ or ‘the weather is bad, more poison puddles for ya muhahaha’, or quest givers. Not every run, some lower 1-5% chance would be fine and interesting. Not it’s kinda straightforward: enter echo - follow cursor with (?), kill it, exist.
thats all for now, imho of course, thanks for the game.